Method of producing a brush track for an adjustable sliding brush transformer

ABSTRACT

AN ADJUSTABLE SLIDING BRUSH TRANSFORMER WITH A RELIEFPOLISHED BRUSH TRACK. THE BRUSH IS FORMED OF A SERIES OF COMVEX CONTACT SURFACES ON SUCCESSIVELY DISPOSED ADJACENT WIRE TURNS. THE SERIES OF CONVEX CONTACT SURFACES IS UNDERSPANNED BY A SERIES OF CONCAVE SURFACES OF RESIN INSULATING MATERIAL ALONG THE BRUSH TRACK. ELECTRICAL CONTACT BETWEEN THE BRUSH AND THE WINDING IS   ACHIEVED BY SLIDING MOVEMENT OF THE BRUSH ALONG THE CONVEX CONTACT SURFACES. THE CONCAVE-CONVEX BRUSH TRACK IS PRODUCED BY RELIEF POLISHING A PRESELECTED PORTION OF THE WINDING. A POLISHING DISC CONSISTING OF A MAT OF GLASS FIBERS OR FIBERS OF THERMOPLASTIC POLYAMIDE IMPREGNATED WITH SILICON-CARBIDE GIRT MAY BE USED.

Nov. 30, 1971 H. J. PROXMIRE 3,623,279

METHOD OF PRODUCING A BRUSH TRACK FOR AN ADJUSTABLE SLIDING BRUSH TRANSFORMER Original Filed Nov. l6, 1967 :2 Shoots-Shoot 1 P105? APT [nwrnzfar fling J praxm/re, y t t'orfney.

Nov. 30, 1971 H. J. PROXMIRE 3,623,279

METHOD OF PRODUCING A BRUSH TRACK FOR AN ADJUSTABLE SLIDING BRUSH TRANSFORMIJIR Original Filed Nov. 16, 1967 :3 Shoots-Sheet 2 57flT/ON 49 w- 50 42 I G j [El g 3 4, I I I I I I l-l LL J, g I i j L Lil n 54 l 42 L 43 49 39 40 k F7 .5 a! I! n 2! g w. 36 48 47 a\7 "lllilllllll' ll 55 [n vendor: Harry proxm/rc,

fly 214100 Atto rwa g- United States Patent 3,623,279 METHOD OF PRODUCING A BRUSH TRACK FOR AN ADJUSTABLE SLIDING BRUSH TRANSFORMER Harry J. Proxmire, Fort Wayne, Ind., assignor to General Electric Company Original application Nov. 16, 1967, Ser. No. 683,627, now Patent No. 3,478,2M), dated Nov. 11, 1969. Divided and this application June 30, 1969, Ser. No. 853,578 Int. Cl. B2411 1/00 U.S. Cl. 51328 4 Claims ABSTRACT OF THE DISCLOSURE An adjustable sliding brush transformer with a relief polished brush track. The brush track is formed of a series of convex contact surfaces on successively disposed adjacent wire turns. The series of convex contact surfaces is underspanned by a series of concave surfaces of resin insulating material along the brush track. Electrical contact between the brush and the winding is achieved by sliding movement of the brush along the convex contact surfaces. The concave-convex brush track is produced by relief polishing a preselected portion of the winding. A polishing disc consisting of a mat of glass fibers or fibers of thermoplastic polyamide impregnated with silicon-carbide grit may be used.

This is a division of application Ser. No. 683,627, filed Nov. 16, 1967 now US. Patent No. 3,478,290 issued Nov. 11, 1969.

BACKGROUND OF THE INVENTION This invention relates generally to adjustable sliding brush transformers and more particularly to adjustable sliding brush transformers having an improved brush track arrangement and to a method for producing brush tracks for adjustable sliding transformers.

Conventional adjustable sliding brush transformers consist of a transformer winding wound on a suitable magnetic core, usually of annular configuration. Generally the transformer is arranged to function as an autotransformer and includes a brush holder carrying one or more electrical brushes that slide across and make electrical contact with a brush track. To vary the output voltage of the transformer, the position of the brushes with respect to the brush track is changed either manually or by a motor.

In the manufacture of such prior art adjustable sliding brush transformers, insulated wire is wound on the annular core, and the brush track is formed by lapping or grinding the portions of the insulated winding to be contacted to remove the insulation therefrom and to provide a fiat contact surface for the brushes. Heretofore it has been assumed that it is necessary to provide a flat planar surface on the conductor of the insulated wire in order to provide suitable surfaces for making electrical contact with the brushes.

It will be appreciated that in the process of lapping or grinding not only is a portion of the insulation coating of the winding removed but appreciable amounts of the conductor material. In many instances, as much as one third of the cross-sectional area of metallic conductor of the insulated wire is removed in the process of forming the brush track. A common difficulty experienced in lapping or grinding, particularly in transformer designs with a conductor wire of .0201 of an inch or less in diameter, is that misaligned conductors may be either undercut or overcut in the process. As a result, such transformers during manufacture are rejected as failing to meet quality standards and must be reworked or scrapped.

3,623,279 Patented Nov. 30, 1971 Another disadvantage of such conventional lapping and grinding techniques for producing a brush track or adjustable sliding brush transformer is that lapping and grinding is a relatively expensive step in the process of manufacture. It is, of course, desirable to reduce the cost of manufacturing a product and to improve its quality and performance.

Accordingly, it is a general object of my invention to provide an improved brush track arrangement for an adjustable sliding brush transformer that does not have the disadvantages of the prior art construction.

Another object of the invention is to provide a method for producing a brush track for an adjustable sliding brush transformer wherein the need for a lapping or griding operation to form the brush track is eliminated.

SUMMARY OF THE INVENTION In accordance with one form of my invention, I have provided an adjustable sliding brush transformer comprising a core of magnetic material having a winding of successively disposed adjacent wire turns wound on the core. The winding is formed with a relief-polished brush track including a series of convex contact surfaces on successively disposed adjacent wire turns. Insulating resin material is disposed between the turns that form the series of convex contact surfaces and defines a series of concave surfaces along the brush track underspanning the convex contact surfaces. The adjustable sliding brush transformer includes at least one electrical brush for sliding electrical contact with the convex contact surfaces of the winding whereby electrical contact between the brush and the winding is achieved by sliding movement of the brush along the convex contact surfaces.

According to another aspect of the invention the brush track for the core and coil assembly of the improved adjustable sliding brush transformer is produced by relief polishing a portion of the winding whereby a portion of the insulation coating on the wire is removed to expose the metallic conductor and form a contact surface. A substantially greater amount of resin between the adjacent turns is removed than metallic conductor to form the brush track on the winding. Preferably, a polishing disc formed of glass fibers or of a mat of fibers of thermoplastic polyamide impregnated with siliconcarbide grit is used to polish the brush track to the desired convexconcave configuration.

An important advantage of the present invention is that it is possible in an adjustable sliding brush transformer having a winding of relatively small wire size to provide a brush track characterized by longer service life. Moreover, the brush track can be readily and inexpensively produced as compared with prior art techniques.

The subject matter which I regard as my invention is set forth in the appended claims. The invention itself, however, together with further objects and advantages thereof may be better understood by referring to the following description taken in connection with the accompanying drawings in which:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of an adjustable sliding brush transformer embodying one form of the present invention;

FIG. 2 is an enlarged fragmentary cross-sectional view taken along lines 2-2 of FIG. 1;

FIG. 3 is a view corresponding to the one shown in' FIG. 2 illustrating a prior art brush track arrangement; FIG. 4 is a plan view of an apparatus embodying my improved method for producing a brush track; and

FIG. 5 is a front elevational view of the apparatus shown in FIG. 4, the phantom outline indicating the polishing disc in the elevated position.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now more specifically to FIGS. 1 and 2 of the drawings, I have illustrated therein an adjustable sliding brush transformer embodying one form of my invention. The adjustable sliding brush transformer 10 has an annular core 11 made by winding a ribbon or sheet of magnetic iron or steel. The annular core 11 is enclosed in two generally cup-shaped winding forms 12, 13 made from insulating material, such as plastic. The forms 12, 13 serve as a shell to insulate a winding 14 of successively disposed adjacent turns wound over the forms 12, 13 and may have serrations (not illustrated) along the outer edges to provide guides for placing and holding the insulated wire 15 of the winding 14. i

For a more detailed description of the construction of adjustable sliidng brush transformers of the type in which the present invention may be utilized, reference may be had to U.S. Pat. No. 3,160,841 granted to LP. Stefani et al., U.S. Pat. No. 3,160,842 granted to C.A. Neumann et al., and U.S. Pat. No. 3,185,948 granted to HJ. Helberg, all assigned to the assignee of the present invention.

The winding 14 on the adjustable sliding brush transformer 10 is formed by winding insulated wire about the annular core 11. A brush track 16 is provided on the outer surface of winding 14 for engagement with a brush 17 carried by a brush holder 18. Although in the illustrated embodiment of my invention the brush track 16 lies in a plane substantially perpendicular to the longitudinal axis of the winding 14, it will be appreciated that the brush track may be placed at other locations, as for example, along the outer cylindrical surface of the windmg.

The brush 17 is conventionally constructed from a high resistance carbon or graphite type material to prevent excesisve current flow when adjacent turns of the winding 14 are short circuited. It will be seen in FIG. 1 that the brush holder 18 is secured to a rotatable shaft 19 extending through an opening in the core 11. In order to maintain a predetermined amount of contact with the brush track 16, the brush is urged against it by a spring means 20. The shaft 19 may have mounted thereon a knob 21 to allow manual turning of the shaft for varying the position of the brush 17 along the brush track 16.

Turning now to FIG. 2, I have illustrated therein one form of my improved brush track arrangement. It will be seen that the individual conductors of the winding are bonded to the insulating forms 12, 13 by a resin material 22, such as an epoxy resin. The brush track 16 includes a series of convex contact surfaces 23, which in the illustrated embodiment of my invention were formed by relief polishing the winding 14 to dislodge portions of the insulation coating 24 of the winding 14 and expose the metallic conductor 25 so that an electrical contact between the brush 17 and the winding 14 is achieved by sliding the brush 17 into engagement with the metallic conductor 25 of the convex contact surface 23. It will be noted that as long as the contact surfaces 23 are not worn down by the sliding action of the brush 17, the contact established between the brush 17 and individual convex contact surfaces 23 is essentially linear.

In the process of relief polishing the winding 14, substantially greater amounts of insulating resin material 22 are removed than metallic conductor 25. As a result, the resin material 22 along the track 16 presents a series of concave surfaces 26 that underspan the series of convex contact surfaces 23. An advantage of this arrangement is that an undercut commutating brush track is achieved without having to individually grind down the insulating material between contact surface 23.

In FIG. 3 I have illustrated a commonly used brush track arrangement of the prior art. The brush track 28 is formed by removing the insulation from the insulated wire 29 by grinding and lapping so as to provide a series of relatively flat contact surfaces 30 for travel of the brush 31. In order to obtain the desired flat contact surfaces 30, an appreciable quantity of metallic conductor 32 is removed. To augment brush track life, the contact surfaces 30 may be plated with a layer of a corrosion resistant metal or alloy, such as gold.

It will be noted that along the brush track 28 shown in FIG. 3, the resin material 33 between the flat contact surfaces 30 is generally flush with the fiat contact surfaces 30. As wear occurs on the contact surfaces 30, it will be apparent that the brush 31 when moved over the surface of the resin material 33 will dislodge particles of the resin material 33, and the contact surfaces 30 and the brush will become contaminated with the particles.

I have found that in adjustable sliding transformers that use conductor wire of relatively smaller sizes the contact surfaces of the brush track do not have to be flat to provide satisfactory performance and service life. Also, economies in the manufacture and improved performance can be achieved by a method of relief polishing which I will now more fully describe.

Having more specific reference now to FIGS. 4 and 5, I have illustrated therein the improved method of producing a brush track for an adjustable sliding brush transformer as exemplified in a turntable apparatus 36. The apparatus 36 is comprised of a turntable 17 rotatably supported on a frame 38, a first and a second mandrel assembly 39, 40, a mandrel drive motor 41, and a polisher assembly 42.

To carry out the steps of the method for producing a brush track, an operator stands at the left side of the apparatus 36 as viewed in FIG. 4 or adjacent to the loading and unloading station. At this station controls (not shown) are conveniently positioned so that the operator can cause the turntable to rotate degrees to move a core and winding assembly 48 from the loading and unloading station to the polishing station.

When the turntable 37 is in a position shown in FIG. 4, polishing disc 43 of the polisher assembly 42 is lowered mto engagement with the portion of the winding on which the brush track is to be formed, and a friction wheel 44 connected to mandrel assembly 40 is engaged with a friction wheel 45 driven by motor 41. In the illustrated embodiment of my invention, the motor 41 drives the friction wheel 45 at a speed of five revolutions per minute. In the specific exemplification of my invention, it was found that in two revolutions the desired relief polishing was accomplished. It will be noted that friction wheel 46 at the loading and unloading station is not drivingly engaged with friction wheel 45 of motor 41 and becomes engaged with it only when it is at the polishing station. After the brush track is produced by relief polishing at the polishing station, the turntable 37 is rotated by the operator to move the completed core and winding assembly 47 to the loading and unloading station where it is lifted oif the mandrel assembly 39, and another core and winding assembly is placed in position on the mandrel assembly 39. In the Illustrated embodiment of the invention, polishmg dlsc 43 is driven by an air motor 49 pivotally supported on an arm 50 carried on bracket 51. In order to ad ust the contact pressure that the polishing disc exerts agalnst the winding, an adjustable counterbalance weight 52 is attached to a balance arm 53. When the balance weight 52 is positioned to provide the desired amount of pressure, it is secured by turning the knob 54. At the completion of the relief polishing operation. an air cylinder 55 is actuated to elevate the arm 50 and lift the polishing disc 43 out of engagement with the core and winding assembly. When the next winding and core assembly 48 is indexed into position at the work station, air cylinder 55 is then deenergized, rod 56 of the air cylinder 55 dropping out of engagement with the arm so that the desired amount of contact pressure is now applied as determined by the position of the counterbalance weight 52 on the balance arm 53.

Thus, the method of producing my improved brush track arrangement for an adjustable sliding brush transformer involves relief polishing a portion of the winding of the core and winding assembly until the insulation coating on the wire is removed to expose the bare metallic conductor and to remove a substantially greater amount of the resin material than metallic conductor to form a concave-convex brush track. Although preferably I have employed a polishing disc of thermoplastci polyamide fibers impregnated with silicon-carbide grit, it will be understood that other polishing discs, such as fiber glass, that will remove substantially more resin material than metallic conductor may be employed.

An important advantage of the improved transformer and method for producing a brush track for an adjustable sliding brush transformer as described above is that the quality of the transformer and specifically the brush track is improved as compared with transformers of the prior art having brush tracks produced by lapping and grinding operations. It is possible with the improved arrangement to achieve significant manufacturing cost savings in transformers utilizing relatively fine wire as a result of the reduction in the number of rejects during manufacture.

From the foregoing description of the improved apparatus and method exemplifying my invention, it will be apparent that I have provided an improved variable transformer of the adjustable brush type. Although in the exemplification of my invention, the method was illustrated in conjunction with a brush track having convex contact surfaces, it will be appreciated that my method of producing brush tracks by relief polishing can also be employed in connection with brush tracks having flat surfaces to achieve undercutting between the flat contact surfaces. For example, in adjustable sliding brush transformers of the higher current rating using conductor wire of relatively larger diameter size, the contact surfaces may be formed by removing the insulation by grinding the wire flat and then may be relief polished in accordance with the present invention. It will be obvious therefore to those skilled in the art that changes and modifications may be made without departing from the invention. It is therefore intended in the appended claims to cover all such changes and modifications that fall within the true spirit and scope of my invention.

I claim:

1. A method of producing a brush track for a core and winding assembly of an adjustable sliding brush transformer, said core and winding assembly including an annular core of magnetic material, a shell of insulating material on said annular core and a winding of wire having an insulation coating and a metallic conductor on said annular core, said winding having at least a portion thereof bonded by resin material disposed between adjacent turns thereof, said method comprising the steps of: imparting a predetermined amount of rotation to the core and winding assembly and simultaneously relief polishing a portion of said winding to remove a portion of the insulation coating on said wire to form a series of contact surfaces and to remove substantially greater amounts of resin material from between adjacent turns of the winding than of said metallic conductor to form a brush track on said winding.

2. The method set forth in claim 1 wherein said polishing is performed by a disc comprised of a mat of fibers of thermoplastic polyamide impregnated with silicon-carbide grit.

3. A method of producing a brush track for a core and winding assembly of an adjustable sliding brush transformer, said core and winding assembly including an essentially annular core of magnetic material and a winding formed of wire having an insulation coating and a metallic conductor, said winding being wound on said core and having at least a portion thereof bonded by resin material, said method comprising the steps of: relief polishing a portion of said winding to remove a portion of the insulation coating on said wire to expose said metallic conductor and form a series of contact surfaces and to remove a substantially greater amount of resin material from between adjacent turns of the winding than said metallic conductor to form the brush track.

4. The method set forth in claim 3 wherein the said step of relief polishing is carried out by rotating a polishing disc comprised of a mat of fibers of thermoplastic polyamide impregnated with silicon-carbide grit.

References Cited UNITED STATES PATENTS 1,361,883 12/1920 Littman 51108 2,118,267 5/1938 Richter 338-174 X 2,671,913 3/1954 Kirsch 51108 X 2,949,592 8/1960 Smiley 336148 3,293,582 12/1966 Schmitt 29602 X 3,486,220 12/1969 Braun 51281 X DONALD G. KELLY, Primary Examiner US. Cl. X.R. 51105 R 

